This invention relates to a gasket for a hopper outlet, and more particularly to a gasket for use with a pneumatic outlet, as utilized on a covered hopper railway car for unloading a particulate, granular, powdered, or other fluent, solid lading. Covered hopper railway cars are utilized to transport a wide variety of bulk particulate or powdered (fluent) ladings, such as plastic pellets, cement, flour, and the like. As shown in the co-assigned U.S. Pat. Nos. 3,659,752, 3,701,460, 3,715,053, 3,778,114, and 4,114,785, such covered hopper railway cars are often provided with downwardly and inwardly sloping side walls which funnel lading into an outlet attached to the bottom end of the hoppers of the covered hopper car. Such outlets are oftentimes pneumatic unloading outlets so constructed that air can be forced through the outlet in such manner as to entrain the particulate or powdered lading into the air moving through the outlet such that the entrained lading can be pneumatically conveyed from the hopper car.
As can be seen by referring to the above-noted prior art patents, the outlet is conventionally a trough-like weldment, having end walls and side walls sloping inwardly and downwardly toward a conduit through which air is drawn, and in which the lading is entrained in the moving air stream. An outlet frame is provided at the upper portion of the outlet side and end walls, with the outlet frame being generally rectangular. A similar downwardly facing hopper frame is secured to the lower reaches of the inwardly and downwardly extending hopper side and end walls. Typically, the outlet frame is bolted to the hopper frame, with a compressible (i.e., elastomeric) gasket interposed therebetween so as to provide a seal between the hopper and the outlet. This construction is illustrated in FIG. 5 (labelled prior art) of the instant drawings. As can be seen in FIG. 5, there was oftentimes a space S of at least the thickness of the gasket G between the hopper frame and the outlet frame. This space S oftentimes entrapped small quantities of the particulate or powdered lading. Also, the gasket was usually of a relatively soft elastomeric material such that lading particles could become imbedded in the gasket material or be forceably wedged between the gasket and the hopper and outlet frames.
It will be appreciated that such outlets and hopper bottoms are relatively large (e.g., 3 feet .times.6 feet or more) and are made of relatively heavy gauge sheet metal weld construction. While such outlets and hopper bottoms are strong, they are not fully rigid. They are also prone to some warpage during fabrication. That is, upon bolting the outlet frame to the hopper frame, both the hopper frame and the outlet frame may tend to warp or flex (twist) relative to one another.
It is oftentimes necessary to thoroughly clean the inside of a covered hopper railway car before a lading can be onloaded so as to ensure that the new lading is not contaminated by any residue of past ladings or the like. This cleaning process may be done by a workman who enters the car and scrubs the inside of the car, utilizing air or water pressure. However, it has been found that even small quantities of certain ladings can contaminate a new lading, and it is difficult to remove all residual lading, even with thorough cleaning.
For example, a typical covered hopper railway car may carry up to about 190,000 pounds (about 5700 cubic feet) of plastic pellets. However, if the previous lading was red plastic pellets, very small residual quantities of the red pellets (e.g., only a few pellets) have been known to so contaminate a subsequent load of white plastic pellets as to render the quality of the white plastic pellets unacceptable, even though the pellets were of the same resin (e.g., polyethylene). Also, upon changing resins or resin grades even very small, residual quantities of residual resins from prior ladings may contaminate a subsequent lading. Thus, there has been a long-standing problem in constructing railway covered hopper cars which could be readily cleaned, which did not have any unnecessary crevices or the like in which particulate or powdered ladings could become lodged, and which were relatively easy to thoroughly clean.
In my earlier copending U.S. patent application Ser. No. 793,753, filed Nov. 1, 1985, now U.S. Pat. No. 4,768,684 which is herein incorporated by reference, I disclosed two different gaskets, both of which overcame the above-noted long-standing contamination and cleaning problems. One of my prior designs required that the outlet frame be machined so as to have a groove therein which would accept a soft elastomeric gasket. Upon bolting the outlet frame to the hopper frame, a tight metal-to-metal seal was formed inwardly of the gasket so as to prevent the lading from coming into contact with the gasket. However, the requirement of machining a groove in the outlet frame prevented this gasket from being retrofitted to existing outlets.
Further, in my above-noted U.S. Pat. No. 4,768,684, another seal embodiment was disclosed which may be retrofitted to existing outlets. This seal or gasket embodiment utilized an I-shaped metal spacer, tapered across its face from side-to-side, between the hopper and outlet frames with upper and lower elastomer gaskets between the web of the I-shaped spacer and the upper hopper frame and the lower outlet frame. In this manner, a continuous metal-to-metal seal was ensured between the spacer and the frames so as to prevent lading particles from being imbedded in the elastomeric gaskets, and compression of the elastomeric gaskets ensured sealing. While this I-shaped metal member resulted in substantial expense, but it did solve contamination problems and did allow retrofitting.